Generating a Bittorrent Infohash from sha1?

[MichaelJ91]

Thought id ask here is it possible to generate an infohash or magnet link from knowing a sha1 of a file? forgive me if you don't understand what I mean.

[-nelly-]

If you have the SHA-1 of a file, e.g.:

Code:

90cf01baaa749c868aed334cbdf546b9d435c206

Just add the magnet in front of it. e.g.:

Code:

magnet:?xt=urn:btih:

Which will give you the magnet. e.g.:

Code:

magnet:?xt=urn:btih:90cf01baaa749c868aed334cbdf546b9d435c206

[NIK]

I do understand what you mean, and the answer is that no, it isn't possible. An infohash (in it's own right or expressed as a magnet link) is an SHA1 hash of a bencoded set of keys containing among other things a set of SHA1 hashes of "pieces" of files.

You cannot generate an infohash unless you have the original file.

[kjf]

If you have the SHA-1 of a file, e.g.:

An "info hash" is the SHA-1 of the info dictionary part of a torrent file, which will not be the same as the SHA-1 hash of any file within the torrent.

Consider that if you rename a file, the SHA-1 of the file itself will not change, but the hash of a torrent generated after the name change will be different from the hash of a torrent generated before.